1. Field of the Invention
The present invention relates to a technique for implementing a still function of a DVD, and more particularly to an apparatus and a method for accurately implementing a still function of a DVD.
2. Description of the Background Art
FIG. 1 is a schematic block diagram of an apparatus for implementing a still function of a DVD in accordance with a conventional art.
As shown in the drawing, the apparatus for implementing a still function of a DVD of a conventional art includes a system decoder 2 for receiving a data (VOBU) outputted from a DVD reproducing unit 1, decoding it to output A/V bit streams (A/V_EL_ST), and extracting presentation time stamps (PTS); a bit stream buffer 3 for receiving the A/V bit streams from the system decoder 2 and buffering it; an A/V decoder 4 for receiving and decoding the A/V bit streams (A/V_EL_ST) from the bit stream buffer 3, and displaying it according to the presentation time stamps (PTS); and a host computer 5 for receiving an inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST), comparing the inherent number of the A/V bit streams (A/V_EL_ST) with an inherent still frame number (Still_VO_LBN) of a navigation data outputted from the DVD reproducing unit 1, and controlling the A/V bit streams output of the system decoder 2 according to the comparison result.
The operation of the apparatus for implementing a still function of a DVD of the conventional art constructed as described above will now be explained with reference to the accompanying drawings.
First, the system decoder 2 receives the data (VOBU) reproduced and outputted from the DVD reproducing unit 1, decodes the data (VOBU) and stores the A/V bit streams (A/V_EL_ST) in the bit stream buffer 3. In addition, the system decoder 2 extracts the presentation time stamps (PTS) of each video frame from the data (VOBU) reproduced and outputted from the DVD reproducing unit 1 and transmits it to the A/V decoder 4.
When the A/V bit streams (A/V_EL_ST) stored after being received from the system decoder 2 grows to a size of one frame, the bit stream buffer 3 transmits it to the A/V decoder 4.
Then, the A/V decoder 4 receives the A/V bit streams (A/V_EL_ST) from the bit stream buffer 3, decodes and restore it into its original A/V data. And the A/V decoder 4 also displays the restored A/V data on a screen according to the presentation time stamps inputted from the system decoder 2.
When the inherent still frame number (Still_VO_LBN) of the navigation data is outputted from the DVD reproducing unit 1, the host computer 5 compares the inherent still frame number (Still_VO_LBN) with the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) inputted from the system decoder 2.
Upon comparison, if the inherent number (Still_VO_LBN) of the still frame and the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) are identical to each other, the host computer 5 controls the output of the system decoder 2. Under the control of the host computer 5, the A/V bit streams (A/V_EL_ST) corresponding to the video frame to be stilled is stored in the bit stream buffer 3.
Thereafter, when the A/V decoder 4 receives the video frame to be stilled from the bit stream buffer 3 and decodes it, the bit stream buffer 3 is turned to an underflow state, according to which the A/V decoder 4 displays the lastly decoded frame.
In other word, the apparatus for implementing a still function of a DVD in accordance with the conventional art provides a still frame by utilizing a function of most MPEG decoders that when an underflow occurs in the bit stream buffer 3, a frame just prior to the underflow is stopped and displayed.
Generally, in case of a finite still, a still time is defined between 0˜244 ms. Thus, in order to implement a still function accurately, the time point when a command on the still is inputted from an external source must be accurately recognized.
However, in the conventional apparatus for implementing a still function of a DVD by utilizing the underflow of the bit stream buffer, there is a possibility that a frame to be stilled is not stilled due to a delay in the decoding and displaying operation of the A/V decoder. And thus it may cause a problem that a stability of the system is degraded.
In addition, in the conventional apparatus for implementing a still function of a DVD, a delay time that data buffered in the bit stream buffer is displayed is different depending on the internal structure of the A/V decoder, Accordingly, it is difficult to detect at what time point the still occurs.
Therefore, in order to solve the problem, the conventional apparatus for implementing a still function of a DVD, the periodically reads the presentation time stamp of the video frame being displayed after all A/V bit streams of a frame including still information are applied to the system decoder. And the host computer compares the presentation time stamp extracted by the system decoder with the presentation time stamp of the video frame to be stilled and judges whether the currently displayed video frame is a video frame to be stilled.
However, it still has a problem that the A/V decoder should repeatedly perform the comparing operation between the presentation time stamps of the video frame to be stilled and the presentation time stamp of the currently displayed video frame until the frame to be stilled is displayed.